[Coding Standard]: Use self:: instead of class name for static member reference in WP_Http class

[dilipbheda]

This issue proposes a minor refactor to improve code maintainability and ensure proper static context within the class.

Find the following PHPCS error:

phpcs: error
Squiz.Classes.SelfMemberReference.NotUsed - Must use "self::" for local static member reference

Current Code:

WP_Http::normalize_cookies( $parsed_args['cookies'] );

Proposed Change:

self::normalize_cookies( $parsed_args['cookies'] );

[SergeyBiryukov]

In 60191:

Coding Standards: Use self:: for static member reference in WP_Http.

This resolves a PHPCS error:

Squiz.Classes.SelfMemberReference.NotUsed - Must use "self::" for local static member reference

Follow-up to [20767], [37428], [38164].

Props dilipbheda.
Fixes #63346.